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How the Higgs Boson Was Found

Before the elusive particle could be discovered—a smashing success—it had to be imagined

The ATLAS detector, one of two experiments to spot the elusive Higgs boson in particle smashups at CERN’s Large Hadron Collider, weighs as much as a hundred 747 jets and houses more than 1,800 miles of cable.
(Claudia Marcelloni / CERN)

And as the world came to quickly learn, the evidence that the Higgs particle had been detected was strong enough to cross the threshold of discovery. With the Higgs particle now officially found, the audience in Geneva broke out into wild applause, as did our little group in Aspen, and no doubt dozens of similar gatherings around the globe. Peter Higgs wiped away a tear.

With a year of hindsight, and additional data that has only served to make the case for the Higgs stronger, here’s how I would summarize the discovery’s most important implications.

First, we’ve long known that there are invisible inhabitants in space. Radio and television waves. The Earth’s magnetic field. Gravitational fields. But none of these is permanent. None is unchanging. None is uniformly present throughout the universe. In this regard, the Higgs field is fundamentally different. We believe its value is the same on Earth as near Saturn, in the Orion Nebulae, throughout the Andromeda Galaxy and everywhere else. As far as we can tell, the Higgs field is indelibly imprinted on the spatial fabric.

Second, the Higgs particle represents a new form of matter, which had been widely anticipated for decades but had never been seen. Early in the 20th century, physicists realized that particles, in addition to their mass and electric charge, have a third defining feature: their spin. But unlike a child’s top, a particle’s spin is an intrinsic feature that doesn’t change; it doesn’t speed up or slow down over time. Electrons and quarks all have the same spin value, while the spin of photons—particles of light—is twice that of electrons and quarks. The equations describing the Higgs particle showed that—unlike any other fundamental particle species—it should have no spin at all. Data from the Large Hadron Collider have now confirmed this.

Establishing the existence of a new form of matter is a rare achievement, but the result has resonance in another field: cosmology, the scientific study of how the entire universe began and developed into the form we now witness. For many years, cosmologists studying the Big Bang theory were stymied. They had pieced together a robust description of how the universe evolved from a split second after the beginning, but they were unable to give any insight into what drove space to start expanding in the first place. What force could have exerted such a powerful outward push? For all its success, the Big Bang theory left out the bang.

In the 1980s, a possible solution was discovered, one that rings a loud Higgsian bell. If a region of space is uniformly suffused with a field whose particulate constituents are spinless, then Einstein’s theory of gravity (the general theory of relativity) reveals that a powerful repulsive force can be generated—a bang, and a big one at that. Calculations showed that it was difficult to realize this idea with the Higgs field itself; the double duty of providing particle masses and fueling the bang proves a substantial burden. But insightful scientists realized that by positing a second “Higgs-like” field (possessing the same vanishing spin, but different mass and interactions), they could split the burden—one field for mass and the other for the repulsive push—and offer a compelling explanation of the bang. Because of this, for more than 30 years, theoretical physicists have been vigorously exploring cosmological theories in which such Higgs-like fields play an essential part. Thousands of journal articles have been written developing these ideas, and billions of dollars have been spent on deep space observations seeking—and finding—indirect evidence that these theories accurately describe our universe. The LHC’s confirmation that at least one such field actually exists thus puts a generation of cosmological theorizing on a far firmer foundation.

Finally, and perhaps most important, the discovery of the Higgs particle is an astonishing triumph of mathematics’ power to reveal the workings of the universe. It’s a story that’s been recapitulated in physics numerous times, but each new example thrills just the same. The possibility of black holes emerged from the mathematical analyses of German physicist Karl Schwarzchild; subsequent observations proved that black holes are real. Big Bang cosmology emerged from the mathematical analyses of Alexander Friedmann and also Georges Lemaître; subsequent observations proved this insight correct as well. The concept of anti-matter first emerged from the mathematical analyses of quantum physicist Paul Dirac; subsequent experiments showed that this idea, too, is right. These examples give a feel for what the great mathematical physicist Eugene Wigner meant when he spoke of the “unreasonable effectiveness of mathematics in describing the physical universe.” The Higgs field emerged from mathematical studies seeking a mechanism to endow particles with mass. And once again the math has come through with flying colors.

As a theoretical physicist myself, one of many dedicated to finding what Einstein called the “unified theory”—the deeply hidden connections between all of nature’s forces and matter that Einstein dreamed of, long after being hooked on physics by the mysterious workings of the compass—the discovery of the Higgs is especially gratifying. Our work is driven by mathematics, and has so far not made contact with experimental data. We are anxiously awaiting 2015 when an upgraded and yet more powerful LHC will be switched back on, as there’s a fighting chance that the new data will provide evidence that our theories are heading in the right direction. Major milestones would include the discovery of a class of hitherto unseen particles (called “supersymmetric” particles) that our equations predict, or hints of the wild possibility of spatial dimensions beyond the three we all experience. More exciting still would be the discovery of something completely unanticipated, sending us all scurrying back to our blackboards.

Many of us have been trying to scale these mathematical mountains for 30 years, some even longer. At times we’ve felt the unified theory was just beyond our fingertips, while at other times we’re truly groping in the dark. It is a great boost for our generation to witness the confirmation of the Higgs, to witness four-decade-old mathematical insights realized as pops and crackles in the LHC detectors. It reminds us to take the words of Nobel laureate Steven Weinberg to heart: “Our mistake is not that we take our theories too seriously, but we do not take them seriously enough. It is always hard to realize that these numbers and equations we play with at our desks have something to do with the real world.” Sometimes, those numbers and equations have an uncanny, almost eerie ability to illuminate otherwise dark corners of reality. When they do, we get that much closer to grasping our place in the cosmos.

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